The present invention relates to an exposure control device for use with optical reproducing apparatuses such as photographic color printers, CRT printers, laser printers, copy machines and the like, and more particularly to an exposure control device for determining a suitable exposure with which a copy of a color original is optically reproduced.
In an optical reproducing apparatus for making a faithful copy of a color original, often characteristic values of three color images of a color original are detected according to which exposures are controlled by color. For example, in a photographic color printer it is well known to control the exposures in accordance with large area transmittance densities (hereinafter referred to as LATDs) of the three colors, namely blue, green and red, of the color original from which a color print is made.
Meanwhile, based on the concept that the image quality of copies depends on the finished quality of the principal subject image of the copies, exposures usually are controlled so as to make a color print with a good quality of principal subject image. This exposure control method is found in, for example, Japanese Patent Publication No. 55-2,941. The exposure control system taught by this Japanese Patent Publication is featured by controlling the exposure of blue green and red color printing lights by using image characteristic values of the whole image area of the color original and principal image characteristic values. In this exposure control system the principal image characteristic value is obtained by specifying one including the principal subject image of a plurality of sub-areas into which the whole image is divided.
Another exposure control system is known, in which the exposures of three colors are controlled so as to make a color print with a specific part having a predetermined density the specific part being automatically determined by detecting an area of color original having a color which appears as fresh color on its positive image. One such exposure control system is taught for example, in Japanese Patent Unexamined Publication Nos. 52-156,625 and 54-68,632.
One problem with system wherein exposure is controlled based mainly on the principal subject image is that accurate exposure control is difficult to effect because the same exposure calculating formula is used for color originals having various kinds of principal subject images with different sizes and color densities. As a result, it has been difficult to obtain reproduced images with good color balance and proper image quality.
Another problem with systems wherein a principal subject image extent is determined by detecting automatically a part of an image having a flesh color is that, where the color originals include walls or furniture which have a color similar to the flesh color of the human body, they are apt to be taken for a part of the human body and to confuse gray color with flesh color. This color confusion is attributable to changes on standing in the characteristics of the film and the illumination source (day time, evening, fluorescent lamp), resulting quite often in incorrect exposure control in color image reproduction.